If you're a man lacking in energy, low testosterone could be to blame.
Dr. David Daniels, medical director of UnityPoint Clinic of Internal Medicine, said testosterone, a hormone produced in the testes that is responsible for the normal growth and development of the male sex organs, peaks in a male's 20s and 30s and then continually declines as he ages.
In addition to feeling tired, men with hypogonadism or low testosterone may also experience problems with mood, libido and a decrease in bone mass.
"A lot of people are tired, fatigued - males and females," Daniels said. "The question is, 'When is it do to a medical condition like low testosterone?' They really need to see their doctor to sort all of that out."
Depression and other medical illnesses could "camouflage" low testosterone, according to Daniels, but he said the problem could be properly diagnosed given enough time.
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Obesity, he said, also effects testosterone values.
"If they lose weight, they can improve it," he said.
Daniels said the bottom of a 20- or 30-year-old's testosterone range is about 300 nanograms per deciliter (ng/dL), while an 80-year-old man's low during the day would be around 200 ng/dL. The upper limits are 1,000 to 1,200 ng/dL.
Studies show a small decline in serum total testosterone concentration as a man ages. One study showed a declines of about 100 ng/dL from age 20 to 80. In young men, testosterone levels are highest at 8 a.m. and lowest around 8 p.m. There is little variation during the day in elderly men.
Once it's determined that a man's testosterone is low for his age, through blood testing, Daniels said the next step is figuring out if it's caused by the gonads or the hypothalamus or pituitary gland's failure to function properly.
The following testosterone replacement options are available in the United States, according to Daniels:
- Testosterone shots are given every two to three weeks. He said they work well and are inexpensive. Side effects, he said are unlikely, but prostate size and function will need to be monitored.
- Testosterone patches, he said, also work well. Some skin irritation can be expected.
- Testosterone gels (AndroGel, Testim, Fortest and Axiron), which are applied on the body, he said, are the most accepted therapies for low testosterone. Cost may be an issue, as well as transferring the gels to others. A child coming into contact with the substance on a consistent basis could experience virilization or developing male sex characteristics.
 "I think people could learn in time to do (the shots). They're cheaper. They're long-acting," Daniels said. "The gels are the most expensive, but probably the easiest to self-administer."
